Ammunition



Feb. 7, 1961 A. J. DUFFIELD AMMUNITION Filed Sept. 13, 1954 zm/surozc ALBERT J. DUF FIELD BY 6 M &

ATTORNEYS United States Patent AMMUNITION Albert J. Duflield, Rosewood Heights, 11]., assiguor to Olin Mathieson Chemical Corporation, East Alton, 11]., a corporation of Virginia Filed Sept. 13, 1954, Ser. No. 455,745

1 Claim. (Cl. 102-45) This invention relates generally to center-fire ammunition of the type wherein the cartridge case or at least the head thereof (as in the case of a shot shell head) is made of aluminum, and particularly to primer cups for use of such cartridge cases.

In the manufacture of center-fire ammunition, it is customary to provide a primer cup into which the priming materials are charged before the cup is assembled with the ammunition case. The ammunition cases (which may be in the form of a shot shell having a metallic head) are separately formed and provided with a central opening in the head thereof for the reception of the charged primers.

Primer cups are universally made by cutting a circular blank from a strip of suitable copperbase alloy, and thereafter cold-drawing the blank into cup shape. Upon completion of the cold-drawing operation, such cups are ready to be charged with the primer mix and thereafter forced into the primer pocket of the case. While the particular alloy of which a primer cup is made may vary depending upon the composition of the primer mix with which it is to be charged, a well-known and widely used alloy for this purpose is composed of- Such an alloy is cold rolled to a thickness of 0.019" to produce the strips from which the circular blanks are cut for the drawing of shot shell primer cups.

The manufacturing techniques, above referred to, were and are eminently satisfactory for ammunition cases made of copper-base alloy, but in recent years it has become economically desirable to produce such ammunition cases, particularly shot shell heads, of aluminum alloys. Heretofore the same primer cup manufacturing techniques and assembling have been employed with aluminum cases as were previously employed with brass cases. With aluminum cases, it has been observed however that there is a surprisingly large number of rounds which, when fired, show evidence of gas leakage between the primer cup and the adjacent sidewalls of primer pocket in the cartridge case. Accordingly, it is the object of the present invention generally stated to overcome the proclivity of aluminum cartridge cases to leak about the primer cup.

The present invention is predicated upon the discovery that the primer receiving pocket of some aluminum carfridge cases which, after firing, showed evidence of gas leakage also showed evidence of mechanical mutilation upon being disassembled. From this it was reasoned that the mechanical mutilation may have occurred during the process of inserting the primer cup into the cartridge case, and, if so, might be overcome if the hardness of the primer cup were controlled so as to be less than the 2,970,543 Patented Feb. 7, 1961 hardness of the aluminum alloy of which the cartridge case was made. Accordingly, the present invention contemplates that in the manufacture of primer cups for use 111 aluminum cartridge cases, the metal be chosen and treated so as to assure that the hardness of the sidewalls of the primer cup does not exceed the hardness of the aluminum defining the cavity in which the primer cup is to be received. This may be readily accomplished by annealing primer cups of the character heretofore employed.

A typical brass primer cup made of the alloy aforesaid after being cold drawn to cup shape, has a hardness on the exterior of its sidewalls of between and 200 (according to the Diamond Pyramid Hardness scale), but when annealed, by placing in an annealing furnace and being elevated to a temperature of 932 F. over 35 minutes, and then being held at that temperature 30 minutes, has a hardness in the exterior sidewalls of between 74 and 77. This is substantially below the surface hardness of the primer pocket in an aluminum cartridge case, which latter is at least 84 in the cases which I have examined.

For other alloys, the optimum annealing temperature and time period will differ somewhat, but those skilled in the metallurgical art will understand the character of annealing required to reduce the hardness appropriately, it being understood that the essential feature of the present invention is that the hardness of the exterior surface of the primer cup be not in excess of the surface hardness of the primer pocket in the aluminum case, but that the hardness of the primer cup be suflicient to withstand the impact of a firing pin without rupture. As the thickness of the end wall of a primer cup is customarily about forty percent greater than the thickness of the sidewalls thereof and since the end wall is subjected to less cold working in the process of cupping than the sidewalls, the hardness of the end wall will usually be a point or two lower than the hardness of the sidewalls. At an end wall thickness of 0.019 inch, primer cups of the alloy aforesaid which, after annealing, have a hardness at the end wall of 73 adequately withstand the impact of the firing pin.

Primer cups cold-drawn on tools which are in excellent working condition require no further treatment than annealing to overcome the gas leakage heretofore experienced with aluminum cases; but when the drawing tools are in such inferior condition that burrs or sharp edges appear on the drawn cups, it is desirable to burnish the cups before annealing them. A suitable burnishing consists of tumbling the cups in a mixture of emery dust and kerosene.

The accompanying drawing shows the construction of a typical centerfire ammunition case to which the invention is applicable. The drawing is; a sectional view showing a primer cup in assembly with the case of a typical metallic cartridge. The metallic round of ammunition illustrated is provided with a shell 11 having a centrally located primer pocket 12 and a primer cup 13 seated within the primer pocket. In accordance with the present invention, the shell 11 is formed of aluminum, but, otherwise the construction illustrated is as disclosed in US. Patent No. 2,021,498.

Aluminum shot shells and rifle cartridges provided with primers, whose cups were annealed in accordance with this invention, loaded and fired in the usual manner, showed no evidence of gas leakage about the primer cup.

From the foregoing description, those skilled in the art should understand the invention and realize that it accomplishes its object. While the composition of one particular copper-base alloy has been given to illustrate the invention, it is to be distinctly understood that the invention is not limited to that particular alloy, but is applicable to primer cups made of brass, gilding metal, aluminum, or any other metal which is compatible with the priming mix to be employed therein, and within the range of hardness, limited on the one hand by the hardness of the primer pocket in the aluminum cartridge case, and on the other hand by ability to withstand the impact of the firing pin. It is, therefore, to be distinctly understood that the invention is not limited to the details of the embodiment described, but that such modifications and variations as suggest themselves to those skilled in the art may be made without departing from the spirit of the invention or the scope of the appended claim.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

References Cited in the file of this patent UNITED STATES PATENTS 733,638 Gardner July 14, 1903 1,510,590 Fahrenwald Feb. 26, 1920 1,668,951 Dickerman May 8, 1928 

